1. Field of the Invention
This invention regards a device, hereinafter termed a diaphragm bow, designed to segregate or separate liquids in a pipe, as is normally done during cementation work in a petroleum well, where use is often made of liquids having different density, and where mixing of the liquids would cause the cementation to be totally or partially unsuccessful.
2. Description of Related Art.
A petroleum well in which a casting operation is to be carried out will ordinarily contain drill fluid. When the grouting compound, which is slightly more viscous and has a higher density than drill fluid, is introduced at the desired location in the well, there is a considerable risk that the grouting compound may sink into the drill fluid and as a result end up in the wrong place in the well. Another danger is that it will be diluted by the drill fluid, and therefore not form a satisfactory casting.
This situation is well known to personnel working in this area, and several methods have been used to overcome the problem.
According to prior art, a relatively high viscosity liquid is during casting work in wells first pumped down to a location immediately below the location of the casting. The highly viscous liquid forms a very sluggish plug that will prevent the grouting compound subsequently pumped into the well from moving downwards and mixing with the highly viscous liquid or the drill fluid located underneath. In addition to being relatively costly, the method has proven not to work satisfactorily.
When cementing in a liner, a bridge plug may be used. However bridge plugs are not suitable for most of the cementation work that is relevant for a petroleum well.
It is also known to arrange an inflatable plug at the casting location. Inflatable plugs have a much greater field of application than bridge plugs, but have large physical dimensions and are therefore difficult to transport to the site by means of e.g. helicopter. Plugs of this type are relatively costly.
A liquid separating means is described in Norwegian patent 303649, comprising two sets of slats, where each set of slats is fixed to separate bosses connected to a common mandrel. Each set of slats distributed along the periphery of the device, and which at their free end portions are braced against e.g. a pipe wall, are provided with a cloth at these free end portions. The cloth is designed to cover the cross section of a pipe, thereby preventing liquids above and below the device from mixing. The device according to NO 303649 must be adapted to each casting operation and introduced into the well while arranged in the end portion of a lead-in pipe.
For all of the above mentioned methods, with the exception of the case of using a high viscosity liquid, the lead-in pipe must be lowered into the well just to position the liquid separating device. Often, the running in is delayed due to limitations in the pumping capacity.